1. Field of the Invention
The present invention relates to a tension control apparatus which controls a tension of a tape extending from a tape reel in a rotary head type tape player or another tape player which is applied to a VTR or a DAT, and especially to, a tension control apparatus for a tape player which is capable of preventing excessive tape tension from acting due to the sudden vibration in a tension detecting member shortly after an operational condition is shifted to a tape travelling mode.
2. Related Art
FIG. 7 is a plane view showing a tape travelling portion of the rotary head type tape player. On a chassis 1, there are provided a feeding-side reel table 2 and a winding-side reel table 3. On each of the reel tables 2 and 3 there is installed a tape reel in which a tape T is wound. The tape player shown in the drawing is a direct drive type, in which the feeding-side reel table spindle 2 and the winding-side reel table 3 are driven directly by a motor M1 and M2, respectively. A magnetic tape T is pulled and guided by loading posts 4 and 5 to be wound partly on a rotary head device 6. In a play mode, the tape T is sandwiched by a capstan 7 and a pinch roller 8 and, in turn, sent out by the rotational force of the capstan 7. And, a rotary drum of the rotary head apparatus 6 rotates together with a magnetic head so as to perform a recording operation or a playback operation.
A reference numeral 10 denotes a tension arm provided as a tension detecting member. At a front end of the tension arm 10 there is fixedly provided a tension post 11. The tension arm 10 is provided to be rotatable about a shaft 13, and the tension post 11 is pressed against the tape T to contact therewith between the posts 4 and 9. On the tension arm 10 there are provided a pair of magnets 14a and 14b, and on the chassis 1 there is provided a hole element 15 as a sensor which detects a shifting amount of the magnets 14a and 14b.
With the above arrangement, for example in a play mode, the tension post 11 shifts in response to the strength of tension of the tape driven to travel by the capstan 7. The shifting amount is output from the hole element 15 by detecting the magnetic poles of the magnets 14a and 14b. The output from the hole element 15 is input to the servo circuit. Then, by a motor control voltage supplied from the servo circuit, a reverse torque of the feeding-side motor M1 is controlled so that an appropriate tension is applied on the tape T. By controlling the tension of the tape, a magnetic head contact pressure between the tape T and the rotary head device 6 is maintained in an appropriate condition.
In accordance with the above tension control apparatus for the rotary head type tape player, in the condition that the loading of the tape is completed as shown in FIG. 7, at a stop mode the pinch roller 8 departs or is released from both the tape T and the capstan 7 so that the tape feeding force by the capstan 7 is not transmitted to the tape T, and the tension arm 10 rotates in a clockwise direction so that the tension post 11 departs from the tape T. And when the operational condition is shifted to a play mode; i.e. a recording/playback mode, the pinch roller 8 pushes the tape T to the capstan 7 and, at the same time, the tension arm 10 rotates in a counter-clockwise direction by a biasing force of the spring 12 s that the tension post 11 contacts with the tape T, thereby realizing the condition where the tension detection becomes possible through the tension arm 10.
In a switching operation from the stop mode to the play mode, the tension arm 10 is abruptly rotated in the counter-clockwise direction due to the elastic force of the spring 12 and, therefore, the tension post 11 hits the tape T abruptly. Accordingly, a tension detecting output which is detected by the hole element 15 comes to indicate an abrupt change in response to the vibration caused by the sudden movement of the tension arm 10. For example, in FIG. 8, a wave (A) shows a motor control voltage being output from the servo circuit on the basis of the detection of the hole element 15 in the case that the tension post 11 suddenly shifts toward the tape T by the biasing force of the spring 12 shortly after the operational condition is shifted from the stop mode to the play mode.
The steep wave indicated by (A) has the same directional tendency as an output that is produced when the tape tension is too weak, therefore this motor control voltage causes the sudden reverse torque in the feeding-side motor M1 shown in FIG. 7. Thus, upon this reverse torque acting on the motor M1, the motor M1 strongly pulls the tape T. This means that the tape tension is suddenly enhanced in spite of the fact that the tape tension is not weakened. Thus, it results in that the tape T is damaged.